The results of chromosomal analysis in this study indicate that the laboratory shrew lines can be divided into two types on the basis of chromosome number : the 2N=30 type and the 2N=40 type, representing the smallest and largest respectively, of numbers of chromosomes reported in this species thus far. The 2N=30 type is only found in the SRI line originating from a wild population on the west coast of Sri Lanka. However, the wild shrews caught on the east coast of Sri Lanka have been reported to have 2N=32. These facts provide evidence of chromosomal polymorphism within the wild population of shrews in Sri Lanka. On the other hand, the 2N=40 type is composed of the NAGand OKI lines originating from wild populations in Japan as well as the BAN line from Bangladesh. Matings between SRI (2N=30) and Japanese (2N=40) shrews demonstrated that their Fl, F2 and reciprocal backcross progeny were readily produced. The following chromosome numbers were observed in the hybrids : 2N=35 in Fl shrew
… Mores, 2N=33 to 2N=38 in F2 shrews and 2N=30 to 2N=38 in reciprocal backcrosses. All the hybrids had the same total of 48 autosomearms. Those Robertsonean lines were developed from them. 9 pairs of metacentric chromosomes, one pair of submetacentric chromosomes and 4 pairs of small acrocentric chromosomes. Furthermore, the metacentric chromosomes could be easily subdivided in to 2 groups : 5 pairsof large metacentric chromosomes and 4 pairs of small metacentric chromosomes. The large metacentric chromosomes which were not found in the 2N=40 type, are believed to have been formed via Robertsonean fusions among 10 pairs of large acrocentric chromosomes seen in the 2N=40 karyotype. We believe that the SRI shrew, as well as the Robertsonean fusion strain mouse, is a useful laboratory animal for chromosome studies.ではアクロ型10対,2N=30核型では大きなメタ型が5対であった.この相違はSRIとNJとの交配から得られたSNJでも確認でき,常染色体の腕数が共に48であることから,ロバ-トソン型癒合によっているものと考えられた.すなわち2N=40の核型のC群アクロ型10対が,2N=30の核型では大きなメタ型の5対に変化したため常染色体としては10本減少したものである.2N=40のNJと2N=30のSRIとの交配からSNJを育成した.その結果F_1では2N=35となり,交配方法によって2N=30から2N=40の範囲で分離させることができた.このことはF_1では2N=35の配偶子が生産される減数分裂の段階でN=15から20に分離することを示している.こうして現在ではSRIとNAGとの交配群からSNラインを育成しており,それぞれ相異なる染色谷を持ったラインが育成できるようになった.またSRIラインの関しては繁殖成績が芳しくないので,NAGとの交配からバロッククロスによって2N=30のラインの育成も併せて行っている.スンクスでは全ての型の染色体を有しており,マウスのようにアクロ型しか有していない動物に対して,ヒト染色体のモデルとしてはより適しているとも考えられる. Less